Semiconductor process for removing defects due to edge chips of a semiconductor wafer and semiconductor device fabricated thereby

ABSTRACT

A method for removing defects due to edge chips of a semiconductor wafer is disclosed. This method includes forming a molding layer over a semiconductor wafer. The molding layer is patterned to form a plurality of storage node holes, where the plurality of storage node holes include at least one first storage node hole formed on an effective chip area and at least one second storage node hole formed on an edge chip area. First storage nodes and second storage nodes are formed in the first and second storage node holes, respectively. A photoresist pattern is formed on the wafer having the storage nodes. The photoresist pattern is preferably formed to expose the effective chip areas and to cover the edge chip areas. The molding layer is etched, using the photoresist pattern as an etching mask, to expose portions of the first storage nodes.

This patent application is a divisional of U.S. patent application Ser.No. 10/809,076 filed on Mar. 24, 2004, now pending, and claims priorityfrom Korean Patent Application No. 2003-18274, filed on Mar. 24, 2003,the contents of which are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for manufacturing a semiconductordevice and, more particularly, to a semiconductor process for removingdefects due to edge chips of a semiconductor wafer and semiconductordevice fabricated thereby.

2. Description of the Related Art

Most semiconductor chips are formed in a circle-shaped semiconductorwafer. Therefore, the semiconductor chips located at the edge of thesemiconductor wafer may have abnormal patterns. This is due to a defocusor the like that occurs during a photolithography process for formingpredetermined patterns in the edge of the semiconductor wafer.

FIGS. 1 through 6 are cross-sectional views illustrating a conventionalsemiconductor process for forming DRAM devices on a semiconductor wafer.In the drawings, reference characters “A” and “B” represent a main chiparea formed in an inside region of the semiconductor wafer and an edgechip area formed in an edge of the semiconductor wafer, respectively.

Referring to FIG. 1, an interlayer dielectric layer 3 and an etch stoplayer 7 are sequentially formed on a semiconductor wafer 1. The etchstop layer 7 and the interlayer dielectric layer 3 are patterned to formmain chip buried contact holes in the main chip area A and edge chipburied contact holes in the edge chip area B. Main chip buried contactplugs 5 a and edge chip buried contact plugs 5 b are formed in the mainchip buried contact holes and in the edge chip buried contact holes,respectively. A molding layer such as a molding oxide layer 9 is formedon an entire surface of the semiconductor wafer 1 having the buriedcontact plugs 5 a and 5 b. A photoresist layer 11 is coated on themolding oxide layer 9. As illustrated in FIG. 1, the photoresist layer11 has a non-uniform thickness throughout the wafer 1. In other words,the photoresist layer over the edge region of the wafer 1 may be formedto be thicker than the photoresist layer over the inside region of thewafer 1.

Subsequently, the photoresist layer 11 over the edge of the wafer 1 isselectively exposed and removed to expose the molding oxide layer 9 inthe edge of the wafer 1. The edge exposure process is for preventing aclamp that contacts with the edge of the wafer from being contaminatedby the photoresist layer during a subsequent dry etching process. Theexposed edge molding oxide layer has a width of We. Preferably, thewidth We is minimized to increase the number of effective chips formedat the wafer 1. Therefore, although the photoresist layer 11 over theedge of the wafer 1 is selectively removed, the remaining photoresistlayer 11 over the wafer 1 may be still non uniform.

The remaining photoresist layer is then exposed and developed using astorage node mask. Consequently, first storage node openings 11 a andsecond storage node openings 11 b are formed in the main chip area A andin the edge chip area B respectively. The first storage node openings 11a exhibit normal profiles that expose the molding oxide layer 9 in themain chip area A, whereas the second storage node openings 11 b exhibitabnormal profiles that do not expose the molding oxide layer 9 in theedge chip area B. This phenomenon is due to the uneven thickness of thephotoresist layer as described above. In other words, the exposureprocess with the storage node mask is performed within a predeterminedfocus latitude that is suitable for the uniform thickness of thephotoresist layer 11 in the main chip area A. Accordingly, it isdifficult to optimize the focus latitude of light irradiated onto theedge chip area B. As a result, defocus occurs in the edge chip area Band the second storage node openings 11 b show abnormal profiles. Inaddition, the defocus phenomenon in the edge chip area B may be due tothe uneven surface profiles on the edge of the wafer 1, especially, on abevel region of the wafer 1.

Referring to FIG. 2, the molding oxide layer 9 and the etch stop layer 7are etched using the photoresist layer 11 having the first storage nodeopenings 11 a and the second storage node openings 11 b as an etch mask.As a result, first storage node holes 13 a exposing the main chip buriedcontact plugs 5 a are formed in the main chip area A. However, secondstorage node holes 13 b having abnormal profiles are formed in the edgechip area B. As shown in FIG. 2, the second storage node holes 13 b donot expose the edge chip buried contact plugs 5 b. This is due to theabnormal profiles of the second storage node openings 11 b. Thephotoresist layer 11 is then removed.

Referring to FIG. 3, a polysilicon layer and a sacrificial layer formedof a material such as oxide are sequentially formed on an entire surfaceof the semiconductor wafer 1 having the first and second storage nodeholes 13 a and 13 b. The polysilicon layer is conformally formed, andthe sacrificial oxide layer is formed to a sufficient thickness to fillthe first and second storage node holes 13 a and 13 b. The polysiliconlayer and the sacrificial oxide layer are etched back until a topsurface of the molding oxide layer 9 is exposed. As a result, firstcylindrical storage nodes 15 a are respectively formed in the firststorage node holes 13 a, and second cylindrical storage nodes 15 b arerespectively formed in the second storage node holes 13 b. Further,sacrificial oxide layer patterns 17 remain in the first and secondstorage nodes 15 a and 15 b. As shown in FIG. 3, the second storagenodes 15 b adjacent to the edge of the wafer 1 are not in contact withthe edge chip buried contact plugs 5 b.

Referring to FIG. 4, the molding oxide layer 9 and the sacrificial oxidelayer patterns 17 are removed using a wet etching process. Accordingly,inner walls and outer sidewalls of the first and second storage nodes 15a and 15 b are exposed. The second storage nodes 15 b adjacent to theedge of the wafer 1 may be lifted during the wet etching process forremoving the molding oxide layer 9 and the sacrificial oxide layerpatterns 17. The second storage nodes 15 b, which are lifted from thesurface of the wafer, are adhered onto the surface of the main chip areaA, thereby acting as particle sources.

Referring to FIG. 5, a dielectric layer 19 and a plate conductive layerare sequentially formed over the semiconductor wafer 1 where the moldingoxide layer 9 and the sacrificial oxide layer patterns 17 are removed.The plate conductive layer and the dielectric layer 19 are patterned toform a first plate electrode 21 a and a second plate electrode 21 b thatcover a cell array area in the main chip area A and a cell array area inthe edge chip area B, respectively. Consequently, as shown in FIG. 5,the cell array area adjacent to the edge of the wafer 1 has a relativelylow surface profile as compared to a normal cell array area (cell arrayarea in the main chip area A). In other words, there exists a stepdifference H between a top surface of the plate electrode (21 a of FIG.5) in the normal cell array area and a top surface of the plateelectrode (21 b of FIG. 5) in the abnormal cell array area. An upperinterlayer dielectric layer 23 is formed over the semiconductor waferhaving the first plate electrode 21 a and the second plate electrode 21b. The upper interlayer dielectric layer 23 is generally formed of aflowable oxide layer such as a BPSG (boro-phosphor-silicate glass)layer. Nevertheless, the upper interlayer dielectric layer 23 also hasan uneven surface profile, which is due to the step difference H.

Referring to FIG. 6, the uneven surface profile of the upper interlayerdielectric layer 23 may lead to a difficulty in a subsequentphotolithography process. Accordingly, there is a need to planarize theupper interlayer dielectric layer 23 using a planarization process suchas a chemical mechanical polishing (hereinafter, referred to as “CMP”)process. However, when the upper interlayer dielectric layer 23 havingthe uneven surface is planarized using the CMP process, an upper cornerC of the plate electrode in the normal cell array area adjacent to theabnormal cell array area may be exposed as shown in FIG. 6.

As discussed above, the storage nodes in the cell array area that isadjacent to the edge of the wafer may be lifted during a subsequent wetetching process. The storage nodes, which are lifted, are adhered ontothe normal main chip area, thereby acting as particle sources.

Accordingly, the manufacturing yield of semiconductor devices issignificantly reduced. Moreover, the abnormal area where the storagenodes are lifted has a lower surface than the normal cell array area.Thus, the storage nodes in the normal cell array area may be exposedduring a subsequent planarization process.

SUMMARY OF THE INVENTION

The semiconductor processes include forming a molding layer on asemiconductor wafer. The molding layer is patterned to form firststorage node holes and second storage node holes. The first storage nodeholes are formed in a plurality of effective chip areas which aredefined in an inside area of the wafer, and the second storage nodeholes are formed in a plurality of edge chip areas which are defined inan edge of the wafer. First and second storage nodes are formed in thefirst and second storage node holes respectively. A photoresist patternis formed on a predetermined area of the wafer having the storage nodes.The photoresist pattern covers portions of the edge chip areas. Themolding layer in the effective chip areas is selectively etched usingthe photoresist pattern as an etching mask, thereby exposing portions ofthe first storage nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 6 are cross-sectional views for illustrating aconventional semiconductor process.

FIG. 7 is a top plan view for illustrating semiconductor processesaccording to embodiments of this disclosure.

FIGS. 8 through 12 are cross-sectional views, taken along the line I-I′of FIG. 7, to illustrate semiconductor processes according toembodiments of this disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This disclosure will now describe embodiments of the invention morefully hereinafter with reference to the accompanying drawings. FIG. 7 isa top plan view to illustrate processes of fabricating semiconductorchips formed on a semiconductor wafer in accordance with embodiments ofthis disclosure, and FIGS. 8 through 12 are cross-sectional views takenalong the line I-I′ of FIG. 7. In the drawings, reference characters “A”and “B” indicate effective chip areas formed in the inside of thesemiconductor wafer and the edge chip areas formed in the edge of thesemiconductor wafer, respectively. Furthermore, each of the effectivechip areas A comprises an effective cell array area Cm and an effectiveperipheral circuit area Pm surrounding the effective cell array area Cm,and each of the edge chip areas B comprises an edge cell array area Ceand an edge peripheral circuit area Pe surrounding the edge cell arrayarea Ce. Scribe lanes S/L are interposed between the chip areas A and B.

Referring to FIGS. 7 and 8, a lower interlayer dielectric layer 53 andan etch stop layer 57 are sequentially formed on the semiconductor wafer51. It is preferable that the lower interlayer dielectric layer 53 isformed of a silicon oxide layer and the etch stop layer 57 is formed ofa material layer having an etch selectivity with respect to the lowerinterlayer dielectric layer 53. For example, the etch stop layer 57 maybe formed of a silicon nitride layer. The etch stop layer 57 and thelower interlayer dielectric layer 53 are patterned to form buriedcontact holes in the respective cell array areas Cm and Ce. The buriedcontact holes expose predetermined areas of the semiconductor wafer 1.When semiconductor devices formed in the chip areas A and B are DRAMdevices, the buried contact holes expose source areas of accesstransistors in the DRAM cells. Buried contact plugs are formed in theburied contact holes. The buried contact plugs comprise first buriedcontact plugs 55 a formed in the effective cell array areas Cm andsecond buried contact plugs 55 b formed in the edge cell array areas Ce.

A molding layer such as a molding oxide layer 59 is formed on thesemiconductor wafer 51 having the buried contact plugs 55 a and 55 b.The molding oxide layer 59 is preferably formed of a material layerhaving an etch selectivity with respect to the etch stop layer 57. Forexample, the molding oxide layer 59 may be formed of a chemical vapordeposition (CVD) oxide layer. A first photoresist layer 61 is coated onthe molding oxide layer 59. The first photoresist layer 61 generally hasan uneven thickness throughout the wafer 51. In detail, the firstphotoresist layer 61 on the edge of the wafer 51 may be thicker than thefirst photoresist layer 61 on the inside region of the wafer 51. Thephotoresist layer 61 on the edge of the wafer 51 is selectively exposedand developed to expose the edge of the molding oxide layer 59. The edgeexposure area has a first width of W1. It is desirable that the firstwidth W1 has a minimum value within an allowed range in order toincrease the number of the effective chip areas A. Removing the firstphotoresist layer 61 on the edge of the wafer 51 is for preventing aclamp which fixes the wafer 51 during a subsequent dry etching processfrom being contaminated by the photoresist layer 61. Nevertheless, thefirst photoresist layer 61 adjacent to the edge exposure area may bestill thicker than the first photoresist layer 61 in the inside regionof the wafer 51.

The first photoresist layer 61 that remains after the edge exposureprocess is patterned using a storage node mask to form storage nodeopenings. The storage node openings comprise first storage node openings61 a formed in the effective cell array areas Cm and second storage nodeopenings 61 b formed in the edge cell array areas Ce. In this case, thefirst storage node openings 61 a exhibit a normal profile that exposesthe molding oxide layer 59, whereas the second node openings 61 b,especially, the second node openings 61 b adjacent to the edge exposurearea, exhibit an abnormal profile that does not expose the molding oxidelayer 59. This is due to a defocus that is caused by a non-uniformthickness of the first photoresist layer 61. In addition, the defocusmay also be due to the uneven surface profile of the edge of the wafer51, that is, a bevel region of the wafer 51.

Referring to FIGS. 7 and 9, the molding oxide layer 59 and the etch stoplayer 57 are etched using the photoresist layer 61 having the first andsecond storage node openings 61 a and 61 b as an etch mask, therebyforming first and second storage node holes 63 a and 63 b in theeffective cell array areas Cm and in the edge cell array areas Ce,respectively. The first storage node holes 63 a may show a normalprofile that exposes the first buried contact plugs 55 a, whereas thesecond storage node holes 63 b may show an abnormal profile that doesnot expose the second buried contact plugs 55 b, as illustrated in FIG.9. The first photoresist layer 61 is then removed.

Referring to FIGS. 7 and 10, a storage node conductive layer isconformally formed on a surface of the wafer having the first and secondstorage node holes 63 a and 63 b. The storage node conductive layer maycomprise a doped polysilicon layer. Subsequently, a sacrificial oxidelayer that fills the first and second storage node holes 63 a and 63 bis formed on the storage node conductive layer. The sacrificial oxidelayer and the storage node conductive layer are etched back until a topsurface of the molding oxide layer 59 is exposed, thereby forming afirst cylindrical storage nodes 65 a in the first storage node holes 63a and a second cylindrical storage nodes 65 b in the second storage nodeholes 63 b. As a result, sacrificial layer patterns 67 may remain in thefirst and second cylindrical storage nodes 65 a and 65 b.

Alternatively, the storage node conductive layer may be formed tocompletely fill the first and second storage node holes 63 a and 63 b.In this case, the formation process of the sacrificial oxide layer isomitted, and first and second box-shaped storage nodes are formed in thefirst and second storage node holes 63 a and 63 b, respectively.

The first storage nodes 65 a are normally formed to be in contact withthe first buried contact plugs 55 a. On the contrary, the second storagenodes 65 b may be spaced apart from the second buried contact plugs 55 bby the molding oxide layer 59, as shown in FIG. 10.

A second photoresist layer is formed on the semiconductor wafer havingthe first and second storage nodes 65 a and 65 b. The second photoresistlayer is patterned using a blank mask to form a second photoresistpattern 69 that only exposes the effective chip area A. As a result, thesecond photoresist pattern 69 covers the edge chip area B. Further, thesecond photoresist pattern 69 may expose the scribe lane S/L. Prior toformation of the second photoresist pattern 69, the edge region of thesecond photoresist layer may be selectively exposed and developed toform a second edge exposure area having a second width of W2. In thiscase, it is preferable that the second width W2 is smaller than thefirst width W1.

Referring to FIGS. 7 and 11, the molding oxide layer 59 and thesacrificial oxide layer patterns 67, in the effective chip area A, areselectively etched using the second photoresist pattern 69 as an etchmask, thereby exposing inner walls and outer sidewalls of the firststorage nodes 65 a. The molding oxide layer 59 and the sacrificial layerpatterns 67 may be etched using a wet etching technique. The moldingoxide layer 59 and the sacrificial oxide layer patterns 67 in the edgechip areas B are not etched because of the presence of the secondphotoresist pattern 69. Accordingly, the second photoresist pattern 69prevents the second storage nodes 65 b from being lifted. In addition,the surface of the edge chip area B has the same level as the topsurfaces of the first storage nodes 65 a in the effective chip area A.The second photoresist pattern 69 is then removed, preferably by usingan ashing process.

A dielectric layer and a plate conductive layer are sequentially formedon the wafer 1, in which the second photoresist pattern 69 is removed.The plate conductive layer and the dielectric layer are patterned toform dielectric layer patterns 71 and plate electrodes 73, which aresequentially stacked. The dielectric layer patterns 71 and the plateelectrodes 73 are formed to cover the effective cell array areas Cm andthe edge cell array areas Ce. Therefore, the top surfaces of the plateelectrodes 73 in the effective cell array areas Cm and the edge cellarray areas Ce may be located at the same level. A first upperinterlayer dielectric layer is formed on the wafer having the plateelectrodes 73. The first upper interlayer dielectric layer may be formedof a flowable dielectric layer such as a BPSG layer. The surface of thefirst upper interlayer dielectric layer may still have an unevenprofile. This is due to the first storage nodes 65 a in the effectivecell array areas Cm and the un-etched molding oxide layer 59 in the edgecell array areas Ce. Thus, the first upper interlayer dielectric layerin the cell array areas Cm and Ce is selectively and partially etched toform a first planarized upper interlayer dielectric layer 75.Nevertheless, the first planarized upper interlayer dielectric layer 75may still have a global step difference.

Referring to FIGS. 7 and 12, a second upper interlayer dielectric layeris formed on the first planarized upper interlayer dielectric layer 75.The second upper interlayer dielectric layer may be formed of a CVDoxide layer. The second upper interlayer dielectric layer and the firstplanarized upper interlayer dielectric layer 75 are planarized using aCMP process to form a fully planarized upper interlayer dielectric layer77. As a result, the top surface of the fully planarized upperinterlayer dielectric layer 77 shows a flat profile throughout the wafer51. Accordingly, when a metal layer is formed on the fully planarizedupper interlayer dielectric layer 77 and the metal layer is patternedusing a photolithography process, the flat top surface of the upperinterlayer dielectric layer 77 can prevent a process margin from beingreduced by a defocus or an irregular reflection.

As described above, the edge chip areas adjacent to the edge of thewafer are covered with a photoresist pattern during the etching processfor exposing sidewalls of the first storage nodes in the effective chipareas. As a result, the photoresist pattern can prevent the secondstorage nodes in the edge chip areas from being lifted, even though thesecond storage nodes are spaced apart from the second buried contactplugs.

While the invention has been disclosed in its preferred form, thespecific embodiments thereof as disclosed and illustrated herein are notto be considered in a limiting sense. Indeed, it should be readilyapparent to those skilled in the art in view that various changes inform and details may be made therein without departing from the spiritand scope of the invention as defined by the appended claims and theirequivalents.

1. A semiconductor device produced by a process comprising: forming amolding layer over a semiconductor wafer; patterning the molding layerto form a plurality of storage node holes, wherein the plurality ofstorage node holes include at least one first storage node hole formedon an effective chip area and at least one second storage node holeformed on an edge chip area; forming first and second storage nodes inthe first and second storage node holes, respectively; forming aphotoresist pattern that covers the edge chip area; and selectivelyetching the molding layer, using the photoresist pattern as an etchingmask, to expose portions of the first storage nodes.
 2. Thesemiconductor device of claim 1 produced by a process furthercomprising: sequentially forming a lower interlayer dielectric layer andan etch stop layer on the semiconductor wafer prior to formation of themolding layer; and forming a plurality of contact plugs electricallyconnected to the semiconductor wafer, wherein the contact plugs includeat least one first buried contact plug formed in the effective chiparea, and at least one second buried contact plug formed in the edgechip area.
 3. The semiconductor device of claim 2, wherein the etch stoplayer is a material layer having an etch selectivity with respect to thelower interlayer dielectric layer and the molding layer.
 4. Thesemiconductor device of claim 3, wherein the etch stop layer is asilicon nitride layer.
 5. The semiconductor device of claim 1 producedby a process further comprising, wherein the first and second storagenodes have a cylindrical shape: filling the first and second cylindricalstorage nodes with sacrificial layer patterns; and removing thesacrificial layer patterns in the first cylindrical storage nodes whenthe molding layer is etched.
 6. The semiconductor device of claim 1produced by a process further comprising: removing the photoresistpattern; sequentially forming a dielectric layer and a plate conductivelayer overlying the first and second storage nodes; and patterning theplate conductive layer and the dielectric layer to form plate electrodesand dielectric layer patterns.
 7. The semiconductor device of claim 6produced by a process further comprising: forming a first upperinterlayer dielectric layer on the wafer having the plate electrodes;partially and selectively etching the first upper interlayer dielectriclayer on the plate electrodes to form a first planarized upperinterlayer dielectric layer; forming a second upper interlayerdielectric layer on the first planarized upper interlayer dielectriclayer; and planarizing the first and second upper interlayer dielectriclayers to form a second planarized upper interlayer dielectric layer. 8.The semiconductor device of claim 7, wherein the first upper interlayerdielectric layer is a flowable dielectric layer.
 9. The semiconductordevice of claim 8, wherein the flowable dielectric layer is aborophosphosilicate glass (BPSG) layer.
 10. The semiconductor device ofclaim 7, wherein the second upper interlayer dielectric layer is achemical vapor deposition (CVD) oxide layer.
 11. The semiconductordevice of claim 1, wherein the photoresist pattern exposes the effectivechip area.
 12. The semiconductor device of claim 1, wherein selectivelyetching the molding layer is performed after forming the photoresistpattern that covers the edge chip area.